Method oip preparing



Ann. UNSER.

METHOD 0F PREPARING FURNACE LININGS.

APPucATmn mtu ocr. la. |920.

1,429,909, Patent@ sept. 19,1922.

muy

InVen-kor: Magnus Unger, b5 m ,6W

, Hi's Attornead.

Patented Sept. 19, 1922.

UNITED 'STATES ;PATEN T lorries.

MAGN US UNGER, 0F PITTSFIELD, IEASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC ME'rHoD or PnErAnnrGURNAC'E Lmnos;

applica'iion medoctober 13, 1920. serial No. 41'e,i7o...? y E' To alw/iomit ma cm1/cern."

Be it known t at I, MAGNUS UNGER, `a citizen of the United States, vresiding at Pittsfield, county of Berkshire, State j of Massachusetts, have invented 'certain new and useful Improvements in 'Methodsc'f Preparing Furnace Linings,v of which the following is a specification 'hl- The present invention relateslt'o electric induction furnaces. One of theobjec "of my invention is to render the liningf'lnore durable and to facilitate the cuiingiof' tihe lining rior to the operationfofthe gfurnace. The object is also to facilitate'meltingdovn the starting ring or initiall charge. v

The induction furnace linings commonly are made by ramming refractory material, together with suitable binder, aboutagfor'm or templet and then curing the geen'l'il'ning tliusniade b f subjectin 1t to heatf'rom a ring of meta placed in t ie furnace crucble, constituting a secondary Winding of' the furnace. l Y k l i It has been suggested to build the furnace lining about a templet of metal having a contour corresponding to thedesired shape of the furnace chamber and then to utilize the templet for bakinfr out the furnace lining without removing the tem )let and finall melting down the templet. ue 4to the di fcrences in thermal expansion coeiiicients of metals and of the refractory materialsV used for 'furnace linings the linin is very apt to be cracked when the temp et is heated; Furthermore in attempting to melt ldown thc templet by inducing u. current therein, the pinch effect is likely to prenli'aturely rupture the metal and break the circuitfbc-l fore the lining is fully baked out. The rei pair of such a break in the circuit is a very difficult and time consuming matter.

In accorda-nce with my present invention the green furnace lining 1s shaped in any desired way and then baked out by a composite heater conforming, in a general way, to the contour of the lining but spaced away therefrom and consisting of rings of metal of di ffercnt melting points. The pinch force is not likely to rupture the metal circuit unless thc metal is near or above its melting point. In case the circuit Vof metal having the lowest melting point should be ruptured there will be suiicient heat generated in the circuit having the higher melting point to cause themetal-in the ruptured circuit to melt. 4

I In the Vaccompanying drawing, Fig. 1 isA A a vertlcal section through-anvinduction furnace illustrating d 'first stageof the bakinout of 4a furnace `a composite heater in the crucible; Fig. 2 isa. sec ion of the furnace vCrucible s'howingthe secondfstage of a preparation of the Crucible; and'Fig.l 3 is a sectional view'illustratingthe third-and final stage. i vi The fui'nacecruciblesliownilf Fig. 1 oomnface iliing'.' For ex'amplel inner layer munxture ,of magnesio magnesia whichf has been highly sintere'd short o f fusion@ These ,two materials in a 4,i'iiiissi -uzwalld of fifieebiicksm-roundng: u. 4mass, j of i refractory material 2k consistin of liighl lrefractory material suitable for; ur-

chloridefor sulphate,.are rammed into osil i tion about a templet-of desired form. refc'rably, a spacer is placed between the wall l andthe .lining2 and ivlien thelining has been rammed intoApositionthisfspaoer 1s re moved and thespacelrlledwith somesuitable powdered or iocculentrefractory ymaf ferial as indicated gt3. Powdered magnesia in the sinteredfs'itaie maybe used. '.Tljris loose la er erxnits the lining layer 2xt() -expand Wien lient/ed,- 5 1 y hen tliein'nerlcore .or templet has been removed leaving anannular chamberx4a plurality of startling rings 5 and 6 aigelplai-,ed u'ithin the chamber, L these. rings .being sha ed so .as toconform in a generalway witi the configuration of ,the lining but leaving a space between the side Walls of the chamber 4 and the sides of the rings particularly adjacent the upper ring. These rings 5 and 6 consist of metals melting at ditfer ont temperatures. When the furnace is to be used for production of steel, I prefer to use rings of ferrous metals having different melting points, for example, the upper ring 5 may consist of cast steel and the lower ring 6 of cast iron. In the same manner rings of steel of different melting points may be used.

1V hen the furnace lining has been shaped and the rings have benipla-ced in position` the temperature of the rings is gradually raised by induction in the usual manner (the magnetic core andthe primary winding of the furnace have been omittedfor the sake of simplicity). For example, When'c'uring a linin consisting of magnesia. and tar as -above 5 and 6 is -graduallygincneasediffromfroomr temperature to about 1100 C. through a period of about 18 hours',"th'erby1volat1l1z 1n ture of 1100 the| cast ironring 6 will melt 'allowing the ring" '5 'to Afloat' 'in fthe molten cast iron as indicated in Fig. Duringfth'ev periodthiiltfthe*4 ste'e ring 5 remains ixnffusd'f 'slli'd' f 1ontii ALIlpon 'the molten mass7,th'e molten nss' 'lnthe bottom of f the Crucible' `is tolb'eopen-circuted by lthe pin-ch effect. In case .there should'- be -a 'breakin the: upper ringjthe 'bren-lr will-'tbe b'lsed'j immediately f by" 'the metal of the-lower melting-Point."

The temperature fnall is graduallyi'inby increiisil'igr ."t`e" ':'u'rr' ent in the :'plilr'la'ry of the'fiince so as' to bringthe temperature up to about 1450? Ciduin'g 'the `period off about 49 ho'u'rsi lthis 4texn'p''ra- 'thecastiron producing arnolten charge as indicated at 8* in 'Figi 3; The 'temperature is Vnow raised over'an' 'additional period of about2hours to'aboit 1'55Q C.

' is then ready -for use.

Wht'liclaiin'as ne'v'v and desireto secure by Letters Patent f"the"United-States, is:

1.` 'Th'e' method' fof-starting an in'duction furnace whichconsists-in'placing within the heating 'space of-'s'aid furnace a. lnrality of closed conductors respectivel' -m'e tine at different temperatur-es', and in ucing allie-.ating current-'therein ofsuicient power to successive'ly melt said conductors.

2. The" method of starting an induction furnace which consistsin placing within the heating space of said furnace a cast-iron ring, and a. larger ring of cast steel, melting said cast-iron ring by induced current and thereupon melting said cust steel ring.

3. The method of )reparing for use a green lining for an in uction furnace which consstsin subjecting said lining to the heatescribed,-,the temperature of the rings.-

.saidr heater suicient to bake out said lining,

and carbonizino' the tar binder and ot ierwlse curm the 2: Atatem'peraiVA The furnace ing effect of a compound heater haring a, surface contour conforming substantially to the-contour Vof said lining but spaced away therefrom, said body consisting in larger part of a ring of steel 'and in lesser part of `Aa ring of cast iron, inducing a current in and finally successively melting the parts sivelythe constituents of said body.

5. The method ofpreparino' linings for l"elec'tx'iic:induction furnaces w iieh consists in shal'p'ing a lining material around "aftcni- ;[ilt' of'd'esired form', removing said ten'iplet e'walls of 'the lin 'ing'when heated, inducing' a heating curfrent"in,said body vtbalze 'said lining and final-ly 'melting said rings successively to completely consolidate 'said lining.

1 5. method of starting an 'induction furnace with a green' lining which conf si's'tsin charging said furnace with rings of ferrous metal, having different inciting points` heating said 'rings by induction to cure said lining and thereupon melting said rings by induction.

7. The method of'curing the linings of u furnace chan'iber' which consists in'subjccting said lining to the heating effect of a eurrent induced in a pluralit' of inet-al rings consisting of iiniteiiuls incl temperatures above the temperature range in which rolatilizuhle constituents of said lining are eliminati-(l :ind linzilly by snowssive increases of tciiil'iiriitnre inviting said ting at dilfcifi-nt Sli 

